Recently, researches on micro electro mechanical systems (MEMS) devices manufactured by semiconductor process techniques are actively in progress in various technical fields such as displays, printing devices, precision measuring, precision processing, or the like. For example, an optical scanner having a micro structure is drawing attentions in a display field in which light incident from a light source is radiated on a predetermined screen area to implement a video or a scanning field in which light is scanned on a predetermined screen area and reflected light is received to read out image information.
Such an optical scanner refers to one in which a reflective mirror for reflecting light, a support axis for supporting the reflective mirror, and driving means for moving the reflective mirror are implemented as a single chip.
A comb-shaped driver has driving electrodes that are disposed in parallel on the plane of a moving structure or a stage that is a moving object, and fixed electrodes corresponding to the driving electrodes have a structure in which the fixed electrodes are alternately disposed with respect to the driving electrodes while being fixed and are disposed in parallel on the plane surface of the stage along with the driving electrodes.
In order to allow the electrostatic type driver to have a rotational movement in an electrostatic driving condition, a height difference or a slope is required between the driving electrode and the fixed electrode. Since an additional process for causing one of the driving electrode and the fixed electrode to have a different height or an additional process for causing the height to be inclined after making both heights same as each other is required for the comb-shaped driver, it becomes complicated to manufacture the optical scanner.
Methods of forming an initial angle for the driving electrode are as follows.
First, a method may be employed which deposits a polymer between an upper end of a driving electrode and an upper end of a driving portion to connect the driving electrode with the driving portion, and heat-deforms the polymer to shrink the polymer, thereby inclining the driving electrode. There are limits to this method in terms of high speed driving of the optical scanner, complicated manufacturing processes, and a manufacturing reproducibility for forming a constant initial angle of the driving electrode.
Another method is to have a rotational spring subjected to plastic deformation using Joul-heating while the spring is intentionally inclined to form an initial angle. There is a limit to this method in terms of the driving angle because the optical scanner can only be driven in uni-direction at the time of electrostatically driving the optical scanner.
Yet another method is to form an initial angle using an assembly. According to this method, an additional separate structure needs to be coupled to an optical scanner in order to form the initial angle for the driving electrode, which thus causes the manufacturing process to be complicated and the manufacturing cost to be increased. In addition, a volume of the optical scanner is inevitably increased due to the added structure. Moreover, since a spring of the driving portion and a hinge of the fixed electrode are structurally connected to each other, the spring of the driving portion and the driving electrode also simultaneously rotate when the fixed electrode is inclined, so that the initial angle is not formed. Accordingly, in order to prevent the driving electrode from being rotated, the spring of the driving portion needs to be intentionally twisted, which causes the spring of the driving portion to have a residual stress even when the optical scanner is not driven. This causes unstable driving such as fatigue failures in the long term and a poor impact resistance to occur in terms of driving the optical scanner.